This invention relates to electronic postage meters, and more particularly to the provision of means for preventing the postage meter from printing a selected postage value until authorization has been given to do so in response to the occurrence of one or more predetermined events, including for example, until a determination is made that a selected postage value is available for printing and the accounting amounts stored in the meter have been changed to reflect printing the selected postage value.
As shown in U.S. Pat. No. 4,266,222 issued May 5, 1981 to A. B. Eckert, et al and assigned to the assignee of the present invention, electronic postage meters have been provided with microcomputer systems which include a keyboard and display unit for selecting and entering postage values to be printed, an accounting unit for incrementing the postage used amount and decrementing the postage unused amount and changing the control sum amount stored in meter prior to printing the entered postage value, and a printing unit for printing the entered postage values. Such meters have been provided with an electronic control system for holding an interposer in blocking relationship with respect to a shutter bar to prevent removal of the shutter bar from a keyway formed in the postage meter's drum drive gear, to thereby prevent the entered postage from being printed by the drum until the completion of the function of accounting for the postage value which is to be printed. In the aforesaid U.S. Pat. No. 4,266,222, although the electronic control system requires the coincidence of signals from both the accounting and printing units for causing the interposer to be moved out of blocking relationship with the shutter bar, there have been instances when unaccounted for postage has been printed due to faulty microprocessor operation having inadvertently and prematurely provided the coincident signals required for such movement of the interposer. Accordingly
An object of the invention is to provide an electronic postage meter including a fault tolerant electronic control system for preventing unauthorized printing of postage values;
Another object is to provide an electronic postage meter with improved means for controlling the operation of the interposing apparatus; and
Another object is to provide an electronic postage meter including a periodically pulsing control signal and an amplifier driven thereby for controlling operation of the interposer.